Along an assembly line, diapers and various types of other absorbent articles may be assembled by adding components to and otherwise modifying an advancing, continuous web of material. For example, in some processes, advancing webs of material are combined with other advancing webs of material. In other examples, individual components created from advancing webs of material are combined with advancing webs of material, which in turn, are then combined with other advancing webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. Once the desired component parts are assembled, the advancing web(s) and component parts are subjected to a final knife cut to separate the web(s) into discrete diapers or other absorbent articles. The discrete diapers or absorbent articles may also then be folded and packaged.
For quality control purposes, absorbent article converting lines may utilize various types of sensor technology to detect various types of defects in the webs and discrete components added to the webs along the converting line as absorbent articles are constructed. Example sensor technology may include vision systems, photoelectric sensors, proximity sensors, laser or sonic distance detectors, and the like. Sensor data may be communicated to a controller in various ways. In turn, the controller may be programmed to receive sensor data and reject or cull defective diapers after the final knife cut at the end of the converting line.
However, the controller may not be able to track the exact locations of defects in the web and corresponding diapers with a very large degree of accuracy due to slow sensor and control loop times. For example, the sensor and control technologies may work asynchronously of each other, thus creating control system accuracy challenges, which may be exacerbated at the high speed production rates of some absorbent article processes. For example, if data from a sensor is received by a controller after a processing cycle has begun, the data will not be evaluated in the controller until after the next input cycle has been reached. As such, a window in time is created during which an event may be sensed but not acted upon in the controller. To compensate, the controller may be programmed to assume that the event happened at anytime within the previous processing cycle. Thus, in order to account for the controller's poor ability to track a defect, it may be necessary to reject a relatively large number large number diapers to the front and the rear of a detected defect location in order to provide a high degree of confidence that the actual defective absorbent article is being rejected. As a result, a large number of non-defective articles may be rejected when attempting to reject defective articles. In addition, compensating for the aforementioned time delays may be further complicated when the communication and processing cycles are asynchronous and variable, which prevents deterministic calculation of the delay between sensor detection of an event and the availability of the data to be evaluated by the processor.